Killing the spores of Bacillus species by molecular iodine

To determine the responses of spores of Bacillus subtilis and Bacillus anthracis surrogate Bacillus thuringiensis Al Hakam to I₂ treatment.

Spores of B. subtilis and B. thuringiensis killed by aqueous 30°C-I₂ could germinate, and their inner membrane (IM) was intact. Spore coats were important in I₂ resistance, DNA-protective proteins were not important, and survivors of I₂ treatment were not mutagenized. Viabilities of I₂ -treated, 90-98% killed spores were much lower on high-salinity media, and the treated spores were more heat sensitive than the untreated spores. Germinated I₂ -killed spores were dead as determined by staining with nucleic acid dyes, and many appeared to have been lysed.

Aqueous I₂ appeared to kill B. subtilis and B. thuringiensis spores such that spores lyse soon after they germinate, and not by causing DNA damage or rupture of spores' IM. I₂ treatment also generated many damaged spores that could only be recovered under nonstressful conditions.

This work shows that spores of the model organism B. subtilis, and B. thuringiensis, a surrogate for B. anthracis spores, exhibit similar mechanisms of resistance to and killing by I₂ . Generation by I₂ treatment of conditionally dead spores indicates that appropriate media are essential to efficiently enumerate viable I₂ -treated spores.